When the guest user tries to switch to other profile, they will be prompted with the security method of that profile (if there is any).

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Like the previous point suggests, make sure you have protected the profiles with a security method such as pin, pattern or password. Otherwise, others can access the profiles on your device which does not have a security method.

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Whenever you remove guest mode, your device will always get switched to the profile which is active before the guest mode is enabled.